Women live longer than men but report more illness and utilize more health services than men. Reasons for this apparent contradiction are unknown, as is information on how recent changes in life style and women's roles are affecting the sex differential in health. Data gathered on two cohorts of men and women in Alameda County, California, by the Human Population Laboratory provide a unique opportunity to explore these issues. This prospective epidemiological study will examine sex differences in health in the Alameda County cohorts as measured by a variety of outcomes, including functional ability, morbidity, and mortality. Numerous explanatory variables will be explored, including sex differences in health practices, social and psychological functioning, perception of health, and health service utilization. These cohorts were originally contacted in 1965 (n=6928) and 1974 (n=3118) and have been followed for mortality status through 1984. Information on functional ability and morbidity were gathered in 1965, 1974, and 1983. These data provide a rare opportunity to integrate information on behavioral and psychosocial risk factors and a variety of health outcomes for both men and women. In addition, data from the two cohorts will be used to explore changes in life style over time and their influence on sex differentials in health.